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A116002 n*phi(n)*phi(phi(n)) is a square. 3
1, 8, 27, 32, 108, 128, 243, 250, 432, 512, 686, 972, 1000, 1331, 1728, 2048, 2187, 2197, 2744, 3375, 3888, 4000, 5324, 6174, 6250, 6912, 8192, 8748, 8788, 9826, 10976, 13500, 15552, 16000, 19683, 19773, 21296, 24696, 25000, 27648, 30375 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..220

EXAMPLE

15552*phi(15552)*phi(phi(15552))=373248^2.

MATHEMATICA

esQ[n_]:=Module[{e=EulerPhi[n]}, IntegerQ[Sqrt[n e EulerPhi[e]]]]; Select[Range[31000], esQ] (* Harvey P. Dale, Dec 16 2011 *)

CROSSREFS

Cf. A055744.

Sequence in context: A354179 A262675 A102834 * A339595 A335988 A097054

Adjacent sequences:  A115999 A116000 A116001 * A116003 A116004 A116005

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 13 2006

STATUS

approved

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Last modified August 10 16:03 EDT 2022. Contains 356039 sequences. (Running on oeis4.)